The present invention relates generally to drill bits for use in drilling subterranean bore holes, and more particularly to a novel drill bit having a housing supporting a plurality of drill rod impact members operative to be progressively advanced as exposed working ends of the drill rods undergo wear during a drilling operation.
It is known in the drilling of bore holes, such as in drilling for oil or other fluids in subterranean chambers, to employ drilling tools, generally termed drill bits, which employ a plurality of percussion bits or cutter heads carried on a rotary framework and axially reciprocated so as to effect impacting of the bits against the subterranean formation in a manner to chip, crush and disintegrate the formation beneath the drill bit. See, for example, U.S. Pat. No. 2,371,248 to McNamara, U.S. Pat. No. 3,144,086, to Kurt et al., U.S. Pat. No. 3,387,673 to Thompson and U.S. Pat. No. 3,682,258 to Kelly et al. In the use of such drilling tools, which also may be termed gang drills, the cuttings are continually removed from the bottom of the bore hole by forcing a fluid, such as drilling mud, down into the bore hole through a drill pipe such that the drilling mud flows beneath the drill bit after which the drilling mud and cuttings are forced back up the bore hole about the drill pipe to the surface.
The gang type drills disclosed in the aforementioned United States patents share the common characteristic that each includes a plurality of down hole drills each of which carries a bit at its lower end on which is mounted a plurality of rock cutting teeth or percussion elements. When the cutting teeth or percussion elements on the various bits have undergone a predetermined degree of wear, the gang drill must be removed from the bore hole and the various bits reconditioned or replaced. The downtime required for such bit reconditioning or replacement plays a significant role in the economics of drilling subterranean bore holes. It thus follows that a gang type drill which extends the operating life of the gang drill while disposed within a bore hole would provide signficant economic advantages, both by reducing the overall time required to drill a bore hole of predetermined depth and in the saving of labor time required to remove the drill and recondition or replace the cutting bits.